Always impressed by the clarity and informativenss of your replies.
Do you know, is it simply the presence of magnesium, irrespective of the salt it's a part of, that causes the duct-relaxing, gut-emptying etc effects? In which case magnesium sulphate and magnesium citrate would presumably be equally effective, but one would be much more palatable than the other. [I assume - I've not tasted magnesium citrate, but I find magnesium sulphate ( Epsom Salts ) really horrible].
Just asking, because I simply don't know how magnesium sulphate has its effect - whether it's the action of the magnesium AND the sulphate working together, or just the magnesium part.